For example, Patent Document 1 discloses a spool valve, which causes a spool to slide inside a valve body thereby to control opening and closing of multiple ports, which communicates between the inside of the valve body and the outside of the valve body. In this way, the spool valve is configured to open and close fluid passages to switch over the fluid passages, to control pressure in the fluid passages, and/or to meter a flow quantity of fluid passing through the fluid passages.
In a conventional spool valve, multiple ports include, for example, a first port, which is on the most one end side in the axial direction. That is, the first port is located on the side closest to the one end in the axial direction. A spool mainly slides on the other-end side of the first port. Therefore, a spool hole is formed on the other end side of the first port in the axial direction to have a predetermined diameter. Thus, the spool hole is finished to have a finished diameter.
For example, a manufacturing method for a valve body is conceivable to have a cast hole formation process and a finishing process. The finishing process is to finish a spool hole. Specifically, a cast hole formation process is first implemented to remove a casting core thereby to form a pilot hole for a spool hole on the other end side of the first port in the axial direction. The pilot hole is formed to have a diameter smaller than a finished diameter of the spool hole. In addition, cast holes are formed as ports to intersect substantially perpendicularly to an axial direction of the pilot hole. In the present state, a hole is formed on the one end side of the first port in the axial direction, and the diameter of the hole is greater than the finished diameter.
Subsequently, the finishing process is implemented to cause a cutting tool, such as a drill and a reamer, to cut the inner circumferential periphery of the pilot hole thereby to finish the spool hole to have the predetermined diameter.
It is noted that, the port is at a draft angle. Therefore, in the manufacturing method, it may be concerned that the cutting tool may deflect while the cutting tool is moved in the axial direction. Specifically, as shown in FIG. 9, in the finishing process, a cutting tool 102 is advanced toward a pilot hole 101. A first port 103 is at the draft angle. Therefore, the cutting tool 102 may make contact with the inner circumferential periphery of the first port only on a small diameter side of the first port 103. That is, the cutting tool 102 may cause partial contact with the inner circumferential periphery of the first port on the upper side in the drawing. Consequently, deflection of the cutting tool 102 may make precise manufacturing difficult.
It may be conceivable to implement an additional process before the finishing process of the spool hole to remove a portion of the first port at the draft angle. Nevertheless, the additional process may increase a manufacturing cost for the device.